How to implement VRF

By default ISP routers use one global routing table to forward traffic from different customers. This can lead to some issues like address overlapping, giant routing tables, etc.

To address these needs ISP can use VRF – Virtual Routing Forwarding or VPN Routing Forwarding. Customer interfaces are associated to a specific VPN routing table (secure). One thing to note is that this feature is commonly used with MPLS, when it’s not used with it it’s just called VRF Lite.

VRF Lite it’s easier to implement and to manage in small environments. It’s configured on Layer 3 interfaces, either physical or SVI interfaces.

Let’s have a look at the topology below and it's routing table:

As we can see, all sites can reach each other. 

Let’s start configuring VRF Lite on ISP. Be aware that when you associate the interface to a VRF it will remove ip assignment.

In configuration mode:

ip vrf SITE_A

exit

ip vrf SITE_B

exit

Then we go to interface configuration mode and assign each interface to its VRF:

Let’s check again our routing table:

Testing reachability from ISP to CE.

Things look different right now, see what happens when we specify the VRF name:

As you can see, VRF Lite is very easy to implement and your customer doesn’t need to change anything on his side.

I’ll see on my next post.

Thanks for viewing.

SC